BASF charts commercial path for alternative to conventional air entrainment

Through a microsphere-based agent manufactured at the batch plant, BASF Admixture Systems is positioning producers and their customers to overcome void size and distribution variability long associated with air-entrained concrete mixes, while improving slabs and structures’ freeze-thaw durability.

The company unveiled the Master Builders Solutions-branded technology at ConExpo-Con/Agg 2014 in Las Vegas, indicating pilot applications and standards development activities throughout this year—leading to early-2015 commercial launch. "Microspheres are manufactured at the producer’s plant to provide consistent, stable performance, every time,” says BASF Admixture Systems Technology Manager Paul Seiler. “They are dispensed and uniformly mixed into concrete at a fixed dosage and are the optimal size for freeze-thaw durability.”

The hollow microspheres have highly resilient, tough, but flexible, polymeric shells. Similar to entrained air, they provide stress relief zones for the expansion of freezing water within concrete. But unlike traditional air entrainment, microspheres are not susceptible to variations in ambient conditions, concreting materials, construction practices and other factors that often impact the air void system in finished slabs and structures. In addition, the compressive strength of concrete treated with the microsphere-based admixture technology can be over 30 percent higher than an air-entrained concrete owing to the air content difference.

Dry microspheres have been used successfully in Europe for many years in niche concrete applications, cost of delivery hampering widespread use. With a footprint approximating a pickup truck bed, BASF’s point-of-use manufacturing system and raw material feed make it economically feasible to use the microsphere technology for freeze-thaw durability in lieu of conventional air-entrained concrete. The system produces a tight range of microspheres under 100 microns in diameter.

Dosed at 1 percent by volume, the microsphere-based admixture will enable concrete producers to proportion new mix designs of optimized cement content. Using conventional air-entraining agents to achieve 5 percent to 8 percent air content, producers need to tailor and increase cementitious materials volume to meet compressive strength targets. By eliminating the need for air-entrained concrete and establishing a 1 percent microsphere target volume, the BASF system equates to optimizing fine and coarse aggregate at the expense of higher cost binders.

Aggressive durability testing is under way with microsphere-bearing concrete beams on the shore of Treat Island, Maine—an environment where specimens are assured constant wetting and drying due to reknown Bay of Fundy tides and extensive freeze-thaw exposure. Additional testing is in the works through concrete producers participating in beta phase microsphere manufacturing and specimen preparation.

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